1. Field of Invention
The invention relates to an image forming apparatus that forms an image by transferring a developing agent onto a sheet by electrophotography.
2. Description of Related Art
In a well-known developing device, development is made by electrostatically adhering the toner held on the surface of the developing roller to an electrostatic latent image formed on the surface of the photosensitive drum. In such a developing device, toner leakage often becomes a problem. Due to the toner leakage, the inside of the developing device is smeared with toner, resulting in improper printing, or getting a user""s hand or clothing dirty.
Above all, this tendency becomes high when a non-magnetic one-component agent is used as the toner. Because the toner is mainly held on the surface of the developing roller with the intermolecular force only, even a slightest impact or inclination causes the toner to leak from the periphery of the developing roller.
Generally, sealing members made of a urethane sponge or a PET film are affixed inside the developing device to prevent the toner leakage.
However, to form a high-precision image, a polymerized toner, whose particles are very small in diameter and have a spherical shape with high fluidity, has been generally used in recent years. Because of the high fluidity, the toner leaks from the sealing members.
In most cases, the toner that leaks in such manner is charged insufficiently or uncharged. Therefore, it is apt to be adhered to end portions of the photosensitive member which are out of an area for the image forming. As a result, the toner adheres to an end portion of the sheet, staining the sheet.
Further, the leaked toner soars into a mist and adheres to a wire of the charging device, having a detrimental influence on the discharge. The result is improper charging or the production of electric noise, and the operation of the image forming apparatus becomes unstable.
The invention overcomes the above-mentioned problems and provides an image forming apparatus that produces no deleterious effects on the image quality and the operation of the apparatus in the case of toner leakage.
Because toner migrates toward the ends of the photosensitive drum it is necessary to prevent material or contaminants that accumulate there from being freed so they migrate to the wire of the charging device. To preclude this, covers are provided that extend between the ends of the photosensitive drum and the ends of the wire to prevent free toner from reaching the wire. Further, scraping members are provided in the developing cartridge at each end of the photosensitive drum. The scraper members extend from compartments within the developing cartridge and catch toner that is scraped from the photosensitive drum.